This invention relates to a method of preparing thionyl chloride electrolyte and more particularly to a method of preparing thionyl chloride electrolyte having a water contamination or less than about 1 ppm for use in electrochemical cells.
In recent years a great amount of effort has been exerted in trying to increase the power density of electrochemical cells. Much of this effort has been in the development of batteries of cells which utilize alkali metal anodes and in particular lithium anodes.
In U.S. patent application Ser. No. 419,568, filed on Nov. 28, 1973, and assigned to the assignee of this application there is disclosed an electrochemical cell having a lithium anode and an oxyhalide electrolyte such as thionyl chloride in lithium tetrachloroaluminate or sulfuryl chloride in lithium tetrachloroaluminate. It has been found that it may be desurabke ti reduce the water content of the electrolyte to as low as possible in order to prevent the reaction of any water present with the electrolyte and with the lithium anode.
In this endeavor, it had been found that dry sulfuryl chloride electrolyte that employed lithium tetrachloroaluminate solute could be prepared to have less than 1 ppm of water by allowing the electrolyte to stand over lithium metal. However this technique was not successful when thionyl chloride was used as the electrolyte solvent.
Attempts were made to prepare dry thionyl chloride, SOCl.sub.2, electrolyte compositions by dissolving the LiAlCl.sub.4 in the previously prepared dry solvent or by the situ formation of the salt by the addition of stoichiometric amounts of AlCl.sub.3 and LiCl to the solvent. By either technique, the water contamination was found to be approximately 100 ppm. The use of "dry" solutes in solvent was found to be unemployable.
Thus, it is an object of the invention to prepare dry thionyl chloride electrolyte.
Another object is to prepare thionyl chloride electrolyte having water contamination on the order of only about 1 ppm. for use in electrochemical cells.